Advanced linear motion guide units recently find more extensive applications in any relatively sliding components in machinery as diverse as semiconductor fabricating equipment, machine tools, assembling machines, industrial robots, and so on, and further expected to work with high accuracy while getting smaller and smaller in construction. Encouragement in the recently remarkable downsizing and high-functionality in electronics engineering technology, moreover, calls for the linear motion guide units which can operate with accuracy and high-load capacity even more downsized or compact in construction and further conform to growing demands for high speed operation and high acceleration/deceleration. Especially, the finite linear motion guide unit with cross-roller bearing system is needed to have design for ease of assembly in addition to the downsizing in construction, high-load capacity, high speed operation and high acceleration/deceleration as stated earlier.
Most of prior finite linear motion guide units have a pair of elongated guideway members moveable relatively to each other, and a cage or retainer lying between the guideway members to space away the rollers from each other at preselected intervals The cage or retainer is constituted with a retainer plate which is set to travel over a distance of stroke half the relatively moving stroke of the guideway members. With the finite linear motion guide units constructed as stated earlier, however, the cage or retainer is likely to be off or stray in increments out of a desired location it should be relative to guideway members because of different working conditions including variations in load carried on the finite linear motion guide unit, machining deviations or inaccuracy in the shape of the raceway grooves cut on the guideway members, working geometry where the guide unit operates in an upright posture, high traveling velocity, high acceleration/deceleration, and so on. To cope with the issue stated earlier, most of the finite linear motion guide units have conventionally the cage with means for keeping the cage against straying or wandering from the desired location. A common example of the prior means for preventing the cage from straying installed in the finite linear motion guide units is composed of a rack-and-pinion mechanism in which the cage has a pinion while the guideway members have racks, respectively, so that the pinion comes into mesh with the racks to correct for the relative location of the cage to the guideway members, keeping the cage in place with respect to the guideway members.
In the commonly-assigned Japanese Laid-Open Patent Application No. 2010-236 604, there is disclosed a finite linear motion guide unit designed to carry heavier loads. With the prior finite linear motion guide unit, the smaller pitch or distance between the center-lines of adjacent rollers for rolling elements that are installed in a cage or retainer results in the greater number of the rollers lying in a preselected length of the cage to get an effective raceway area where a raceway groove comes into rolling contact with the rollers as wide as possible to thereby enhance the load-carrying capacity. Moreover, the raceway groove of V-shaped in a transverse section is cut larger in depth to make larger the effective width of raceway surface across which the raceway surfaces of the guideway members come into rolling-contact with the rollers, making certain of the heavier load-carrying capacity. In the prior finite linear motion guide unit, moreover, there is provided a rack-and-pinion mechanism to prevent the cage or retainer from wandering or straying out of a desired location even in high acceleration/deceleration operation. With the rack-and-pinion mechanism as stated earlier, a pinion-holder arrangement is designed to have a size allowed to go in a transverse area of a load-carrying race and the pinion-holder arrangement fits in a window in a cage plate.
With the prior finite linear motion guide unit constructed as stated earlier, however, though the raceway grooves are cut larger in depth as shown in FIG. 2 in the patent literature recited earlier and the cage plate is made as thin as possible to render the raceway surfaces coming into contact with the rollers as large as permitted, there is no provision to retain the rollers in a series of elliptical openings made in the cage plate to fit over the rollers. This means that the rollers are liable to easily fall away from the cage plate of the cage or retainer while in assemblage of the finite linear motion guide unit. As a result, the prior finite linear motion guide unit has been difficult to handle it while in assemblage. With the prior finite linear motion guide unit, moreover, as the pinion-holder arrangement is needed to fit into the window in the cage plate the number of the required parts would increase and the construction would be complicated.
Another commonly-assigned Japanese Laid-open patent application No. 2012-021 572 discloses a finite linear motion guide unit having the construction to retain the rollers in the cage plate for the cage to overcome the shortcomings in the patent literature as stated earlier. With the finite linear motion guide unit in the senior application, however, the cage plate is liable to warp or easily flexible because of too thin in thickness, so that the rollers are apt to easily break up from the cage plate of the cage. Thus, this finite linear motion guide unit is difficult to handle it while in assembling the guideway members with the cage plate having therein the rollers.